Techniques for forming a polymer image by photo-polymerization in which an organic dye is used as a photo-sensitizer (photo-polymerization initiator) are well known, but the sensitivity thereof is generally ISO 10.sup.-3 or less (ISO: International Organization for Standardization), which is far inferior to the sensitivity of silver halide photographic materials. Various methods have heretofore been tried in which a silver halide is used as a trigger and the high amplification degree thereof in a development procedure is utilized for initiation of the polymerization reaction. For instance, Japanese Patent Publication Nos. 46-6581 and 46-16357, Japanese Patent Application (OPI) Nos. 57-138632, 57-142638, 57-176033, 58-107529, 58-169143, and 58-174947 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), and U.S. Pat. Nos. 3,707,379, 3,767,400, 3,782,943, 3,697,275, 3,756,818, 3,687,667, 3,874,947, 3,756,820 and 3,746,542 describe a polymerization method in which the polymerization reaction is initiated by a radical derived from a reducing agent oxidized during development of silver halide. Japanese Patent Publication No. 41-18862 (corresponding to U.S. Pat. No. 3,241,962) describes a polymerization method in which a polymerization reaction is initiated by a radical derived from a peroxide, due to the redox reaction of a silver image obtained by development of a silver halide and a peroxide. Japanese Patent Publication No. 39-2657 (corresponding to U.S. Pat. No. 3,345,164) describes a polymerization method in which the polymerization reaction is initiated by a radical derived from a peroxide, due to the redox reaction of a silver ion as remaining in a non-exposed part and dissolved out therefrom, after development of a silver halide, and a peroxide. U.S. Pat. No. 3,029,145 describes a polymerization method in which the polymerization reaction is initiated by a radical derived from a peroxide, due to the redox reaction of an iron(I)-salt remaining in a non-exposed part, after development of a silver halide with an iron(I)-salt, and a peroxide. Japanese Patent Application (OPI) No. 55-149939 (corresponding to U.S. Pat. No. 4,287,290) describes a polymerization method in which the polymerization reaction is directly initiated by a reducing agent remaining in a non-exposed part, after development of a silver halide.
In these methods, monomers are polymerized in the presence of a radical generated directly or after post-treatment from any of raw materials (silver halide or reducing agent) or products (silver image or oxidation-product of reducing agent) as participated in the development of a silver halide. It is assumed that a polymer image is formed with a sensitivity similar to a silver halide in said methods; however, such methods have the disadvantage that a wet treatment is required in every development of silver halide and polymerization in the presence of a radical. Also, in methods using a peroxide, deterioration of recording materials and occurrence of fog are usually significant during the dark-polymerization to be carried out in the presence of a radical formed by decomposition of said peroxide. In addition, the polymerization reaction requires, in general, a long time period.